PR modula2/111756: Re-building all-gcc after source changes fails to link

PR modula2/111756: Re-building all-gcc after source changes fails to link

When having modula-2 enabled in a development tree and there are any
changes that trigger rebuilds in m2/ doing a 'make all-gcc' in the
build directory might fail due to lack of dependency tracking.
This patch introduces build dependencies into gcc/m2/Make-lang.in using
-M* options.

gcc/m2/ChangeLog:

	PR modula2/111756
	* Make-lang.in (CM2DEP): New define conditionally set if
	($(CXXDEPMODE),depmode=gcc3).
	(m2/gm2-gcc/%.o): Ensure $(@D)/$(DEPDIR) is created.
	Add $(CM2DEP) to the $(COMPILER) command and use $(POSTCOMPILE).
	(m2/gm2-gcc/m2configure.o): Ditto.
	(m2/gm2-lang.o): Ditto.
	(m2/m2pp.o): Ditto.
	(m2/gm2-gcc/rtegraph.o): Ditto.
	(m2/mc-boot/$(SRC_PREFIX)%.o): Ditto.
	(m2/mc-boot-ch/$(SRC_PREFIX)%.o): Ditto.
	(m2/mc-boot-ch/$(SRC_PREFIX)%.o): Ditto.
	(m2/mc-boot/main.o): Ditto.
	(mcflex.o): Ditto.
	(m2/gm2-libs-boot/M2RTS.o): Ditto.
	(m2/gm2-libs-boot/%.o): Ditto.
	(m2/gm2-libs-boot/%.o): Ditto.
	(m2/gm2-libs-boot/RTcodummy.o): Ditto.
	(m2/gm2-libs-boot/RTintdummy.o): Ditto.
	(m2/gm2-libs-boot/wrapc.o): Ditto.
	(m2/gm2-libs-boot/UnixArgs.o): Ditto.
	(m2/gm2-libs-boot/choosetemp.o): Ditto.
	(m2/gm2-libs-boot/errno.o): Ditto.
	(m2/gm2-libs-boot/dtoa.o): Ditto.
	(m2/gm2-libs-boot/ldtoa.o): Ditto.
	(m2/gm2-libs-boot/termios.o): Ditto.
	(m2/gm2-libs-boot/SysExceptions.o): Ditto.
	(m2/gm2-libs-boot/SysStorage.o): Ditto.
	(m2/gm2-compiler-boot/M2GCCDeclare.o): Ditto.
	(m2/gm2-compiler-boot/M2Error.o): Ditto.
	(m2/gm2-compiler-boot/%.o): Ditto.
	(m2/gm2-compiler-boot/%.o): Ditto.
	(m2/gm2-compiler-boot/m2flex.o): Ditto.
	(m2/gm2-compiler/m2flex.o): Ditto.
	(m2/gm2-libs/choosetemp.o): Ditto.
	(m2/boot-bin/mklink$(exeext)): Ditto.
	(m2/pge-boot/%.o): Ditto.
	(m2/pge-boot/%.o): Ditto.
	* README: Remove out of date info.
	* gm2-compiler/M2Quads.mod (BuildStringAdrParam): Correct
	procedure end name.
	* gm2-compiler/SymbolTable.mod (GetVarPointerCheck): Add
	default FALSE return value.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>